- Email: [email protected]
O19 Cortical topographical analysis and source localization of epileptiform discharges
Neurophysiol Clin (1990) 20, S, 7s 9s
7S
© Elsevier, P a r i s
Communications orales
Oral communications
SESSION 3 ModUles exp6rimentaux et informatisds des signaux dectrophysiologiques spontan6s et 6voqu6s
Experimental and computerized models of spontaneous and evoked electrophysiological signals
019 CORTICAL TOPOGRAPHICAL ANALYSIS AND SOURCE LOCALIZATION OF EPILEPTIFORH DISCHARGES R. D. Sidman, D.B.Smith, L.Lee, D.J.Major, The University of Southwestern Louisiana, Lafayette (USA) and the Oregon Comprehensive Epilepsy Program, Portland (USA) We present a method f o r s i m u l a t i n g p o t e n t i a l f i e l d s on the cortical surface. This cortical ~maging ~echnique (CIT) is validated by applying it Eo the potentials evoked by right median nerve stimulation where actual cortical maps are available for comparison. CIT is then applied to several cases of epileptiform discharges where the sites of the discharges have been confirmed. This technique appears to distinguish features of the EEG that are not apparent in standard scalp topographical maps and may make it easier to localize the sources of discharges without recourse to invssive recording techniques.
020 DETECTION
OF RAPID
CHANGES
IN EPILEPTIC
EEG
Gath, I.*, Feuerstein, C.**, P h a m , D.T.*, Bonnet, C.** Vergnes, M.* * *. • Laboratoire L M C / I M A G , UJF, Grenoble. ** Laboratoire de Physiology section Neurophysiology, INSERM U318 CHU, Grenoble * * * Cent ~p ~ Neurochimie, CNRS, Strasbourg. Power spectrum estimation is a useful tool in the quantitative analysis of EEG recorded during epileptic seizures. However, the "epileptic" EEG signal recorded either in experimental animals or in humans might show marked nonstationarity, and hence, estimation of the power spectrum using conventional techniques such as the F F T results in bad estimates, or in "smearing" of the changes due to the averaging process inherent in the F F T technique. A different approach to the estimation of the power spectrum and phase and coherence spectra is based on p a r a m e t r i c modelling of the multichannel EEG. The AR model estimator is required to be efficient in case of short record lengths (2 sec. or less). Continuous recordings of EEG were carried out in a genetically epilepsy-prone rat, and in a normal rat. Recording was made from left and right frontal and occipital leads by implanted electrodes. D a t a acquisition was carried out on IBM P C / A T using a sampling rate of 128 Hz. In addition, several depth recordings (right and left a m y g d a l a and hippocampus) from patients having generalized seizures with focal onset were digitized. Signal segments including both normal EEG and ictal activity were chosen for analysis. Power spectrum estimation and coherence and phase spectra were calculated using multichannel (vectorial) autoregressive modeling, through a process of adaptive segmentation. Thus, estimates of the spectra of quasistationary segments of the signal were obtained. The genetically-prone epileptic rat had abundance of short epochs of multi-spike and spike and wave activity, alternating with normal background activity. 3-D plots of the power spectra and contour maps d e m o n s t r a t e d t h a t the pathological activity could be quantitatively distinguished from periods of normal background activity by spectral peak at around 9-10 Hz, with increased coherence between the different leads. The instantaneous spectral peaks corresponding to the h u m a n seizure were found to decrease gradually in frequency by 2-3 Hz , and together with the coherence spectra gave quantitative information related to the dynamic changes which occur prior and during the seizure. It is argued t h a t power spectrum estimation together with estimation of coherence and phase spectra, using parametric multichanne] modeling of the EEG, could be an aid to the quantitative analysis of EEG during epileptic seizures.
7S
© Elsevier, P a r i s
Communications orales
Oral communications
SESSION 3 ModUles exp6rimentaux et informatisds des signaux dectrophysiologiques spontan6s et 6voqu6s
Experimental and computerized models of spontaneous and evoked electrophysiological signals
019 CORTICAL TOPOGRAPHICAL ANALYSIS AND SOURCE LOCALIZATION OF EPILEPTIFORH DISCHARGES R. D. Sidman, D.B.Smith, L.Lee, D.J.Major, The University of Southwestern Louisiana, Lafayette (USA) and the Oregon Comprehensive Epilepsy Program, Portland (USA) We present a method f o r s i m u l a t i n g p o t e n t i a l f i e l d s on the cortical surface. This cortical ~maging ~echnique (CIT) is validated by applying it Eo the potentials evoked by right median nerve stimulation where actual cortical maps are available for comparison. CIT is then applied to several cases of epileptiform discharges where the sites of the discharges have been confirmed. This technique appears to distinguish features of the EEG that are not apparent in standard scalp topographical maps and may make it easier to localize the sources of discharges without recourse to invssive recording techniques.
020 DETECTION
OF RAPID
CHANGES
IN EPILEPTIC
EEG
Gath, I.*, Feuerstein, C.**, P h a m , D.T.*, Bonnet, C.** Vergnes, M.* * *. • Laboratoire L M C / I M A G , UJF, Grenoble. ** Laboratoire de Physiology section Neurophysiology, INSERM U318 CHU, Grenoble * * * Cent ~p ~ Neurochimie, CNRS, Strasbourg. Power spectrum estimation is a useful tool in the quantitative analysis of EEG recorded during epileptic seizures. However, the "epileptic" EEG signal recorded either in experimental animals or in humans might show marked nonstationarity, and hence, estimation of the power spectrum using conventional techniques such as the F F T results in bad estimates, or in "smearing" of the changes due to the averaging process inherent in the F F T technique. A different approach to the estimation of the power spectrum and phase and coherence spectra is based on p a r a m e t r i c modelling of the multichannel EEG. The AR model estimator is required to be efficient in case of short record lengths (2 sec. or less). Continuous recordings of EEG were carried out in a genetically epilepsy-prone rat, and in a normal rat. Recording was made from left and right frontal and occipital leads by implanted electrodes. D a t a acquisition was carried out on IBM P C / A T using a sampling rate of 128 Hz. In addition, several depth recordings (right and left a m y g d a l a and hippocampus) from patients having generalized seizures with focal onset were digitized. Signal segments including both normal EEG and ictal activity were chosen for analysis. Power spectrum estimation and coherence and phase spectra were calculated using multichannel (vectorial) autoregressive modeling, through a process of adaptive segmentation. Thus, estimates of the spectra of quasistationary segments of the signal were obtained. The genetically-prone epileptic rat had abundance of short epochs of multi-spike and spike and wave activity, alternating with normal background activity. 3-D plots of the power spectra and contour maps d e m o n s t r a t e d t h a t the pathological activity could be quantitatively distinguished from periods of normal background activity by spectral peak at around 9-10 Hz, with increased coherence between the different leads. The instantaneous spectral peaks corresponding to the h u m a n seizure were found to decrease gradually in frequency by 2-3 Hz , and together with the coherence spectra gave quantitative information related to the dynamic changes which occur prior and during the seizure. It is argued t h a t power spectrum estimation together with estimation of coherence and phase spectra, using parametric multichanne] modeling of the EEG, could be an aid to the quantitative analysis of EEG during epileptic seizures.